Apparel for use in applications where under emergency conditions in a hazardous thermal environment might exist should satisfy the following minimum requirements.
A. The fabric from which the apparel is made should be resistant to burning, melting or disintegration on exposure to open flames or elevated temperatures.
B. The fabric should possess good dimensional stability on exposure to elevated thermal conditions since large thermal shrinkages tend to restrict mobility of the wearer.
C. The apparel should function as an effective thermal barrier in order to prevent severe skin burns, and
D. The garments should be durable and comfortable to encourage their use.
It is known to treat normally flammable textile materials, of both natural and synthetic nature, with chemicals such as ammonium phosphate, tetrakis (hydroxymethyl) phosphonium oxides and polymers thereof, and the like to render them fire retardant. Such treatments while effective for rendering fabrics fire retardant under normal conditions of use, such as fabrics designed for use as curtains, rugs, sweaters and the like, are not satisfactory for use under emergency or highly hazardous conditions as in aviators flying suits or apparel designed for use in oxygen enriched atmospheres.
Synthetic materials, such as polybenzimidazoles and polyamides such as poly(m-phenyleneisophthalamides),polyhexamethyleneadipamides and polycaproamides which exhibit improved heat resistance compared to other synthetics such as polypropylene are known and these improved fibers have replaced the more conventional fire retardant materials in many special applications. In applicant's copending U.S. application Ser. No. 230,999 filed March 1, 1972, and now abandoned, it was disclosed that normally flammable fabrics such as fabrics composed of polypropylene and polyamides such as poly(m-phenylene isophthalamides) and the like could be rendered flame proof by the intimate association therewith of a flame proofing amount of a phosphoric acid. It was disclosed also, that although such a flame proofing treatment initially results in fabrics having an Oxygen Index of at least 40, this value was found to decrease on repeated washing of the treated fabric. It was disclosed in the aforementioned application, that the flame proofing treatment disclosed therein could be rendered fast to washing by applying to the treated material a coating of a synthetic resin-material, e.g., polyvinylidene chloride, perfluorinated organic polymers and the like, having an Oxygen Index of at least 40. Such coatings while generally effective on unfinished fabrics, e.g., yard goods and unwoven filaments, are difficult to apply efficiently to finished articles. The coating resin leaves unprotected the seams and other protected areas, such as the overlapping areas of the woven articles. Accordingly, a need still exists for a fiber with thermal characteristics superior to those of the aforementioned fibers and which is fast to washing in water.